Apparatus for mapping and coagulating soft tissue in or around body orifices

ABSTRACT

A probe that may be used to create circumferential lesions in body tissue and, in some implementations, may also be used to perform mapping functions. The probe includes a collapsible/expandable structure that supports electrodes or other operative elements against the body tissue.

BACKGROUND OF THE INVENTIONS

[0001] 1. Field of Inventions

[0002] The present inventions relate generally to medical devices thatsupport one or more diagnostic or therapeutic elements in contact withbody tissue and, more particularly, to medical devices that support oneor more diagnostic or therapeutic elements in contact with bodilyorifices or the tissue surrounding such orifices.

[0003] 2. Description of the Related Art

[0004] There are many instances where diagnostic and therapeuticelements must be inserted into the body. One instance involves thetreatment of cardiac conditions such as atrial fibrillation and atrialflutter which lead to an unpleasant, irregular heart beat, calledarrhythmia.

[0005] Normal sinus rhythm of the heart begins with the sinoatrial node(or “SA node”) generating an electrical impulse. The impulse usuallypropagates uniformly across the right and left atria and the atrialseptum to the atrioventricular node (or “AV node”). This propagationcauses the atria to contract in an organized way to transport blood fromthe atria to the ventricles, and to provide timed stimulation of theventricles. The AV node regulates the propagation delay to theatrioventricular bundle (or “HIS” bundle). This coordination of theelectrical activity of the heart causes atrial systole duringventricular diastole. This, in turn, improves the mechanical function ofthe heart. Atrial fibrillation occurs when anatomical obstacles in theheart disrupt the normally uniform propagation of electrical impulses inthe atria. These anatomical obstacles (called “conduction blocks”) cancause the electrical impulse to degenerate into several circularwavelets that circulate about the obstacles. These wavelets, called“reentry circuits,” disrupt the normally uniform activation of the leftand right atria.

[0006] Because of a loss of atrioventricular synchrony, the people whosuffer from atrial fibrillation and flutter also suffer the consequencesof impaired hemodynamics and loss of cardiac efficiency. They are alsoat greater risk of stroke and other thromboembolic complications becauseof loss of effective contraction and atrial stasis.

[0007] One surgical method of treating atrial fibrillation byinterrupting pathways for reentry circuits is the so-called “mazeprocedure” which relies on a prescribed pattern of incisions toanatomically create a convoluted path, or maze, for electricalpropagation within the left and right atria. The incisions direct theelectrical impulse from the SA node along a specified route through allregions of both atria, causing uniform contraction required for normalatrial transport function. The incisions finally direct the impulse tothe AV node to activate the ventricles, restoring normalatrioventricular synchrony. The incisions are also carefully placed tointerrupt the conduction routes of the most common reentry circuits. Themaze procedure has been found very effective in curing atrialfibrillation. However, the maze procedure is technically difficult todo. It also requires open heart surgery and is very expensive.

[0008] Maze-like procedures have also been developed utilizing catheterswhich can form lesions on the endocardium (the lesions being 1 to 15 cmin length and of varying shape) to effectively create a maze forelectrical conduction in a predetermined path. The formation of theselesions by soft tissue coagulation (also referred to as “ablation”) canprovide the same therapeutic benefits that the complex incision patternsthat the surgical maze procedure presently provides, but withoutinvasive, open heart surgery.

[0009] Catheters used to create lesions typically include a relativelylong and relatively flexible body portion that has a soft tissuecoagulation electrode on its distal end and/or a series of spaced tissuecoagulation electrodes near the distal end. The portion of the catheterbody portion that is inserted into the patient is typically from 23 to55 inches in length and there may be another 8 to 15 inches, including ahandle, outside the patient. The length and flexibility of the catheterbody allow the catheter to be inserted into a main vein or artery(typically the femoral artery), directed into the interior of the heart,and then manipulated such that the coagulation electrode contacts thetissue that is to be ablated. Fluoroscopic imaging is used to providethe physician with a visual indication of the location of the catheter.

[0010] In some instances, the proximal end of the catheter body isconnected to a handle that includes steering controls. Exemplarycatheters of this type are disclosed in U.S. Pat. No. 5,582,609. Inother instances, the catheter body is inserted into the patient througha sheath and the distal portion of the catheter is bent into loop thatextends outwardly from the sheath. This may be accomplished by pivotablysecuring the distal end of the catheter to the distal end of the sheath,as is illustrated in co-pending U.S. application Ser. No. 08/769,856,filed Dec. 19, 1996, and entitled “Loop Structures for SupportingMultiple Electrode Elements.” The loop is formed as the catheter ispushed in the distal direction. The loop may also be formed by securinga pull wire to the distal end of the catheter that extends back throughthe sheath, as is illustrated in U.S. Pat. No. 5,910,129, which isincorporated herein by reference. Loop catheters are advantageous inthat they tend to conform to different tissue contours and geometriesand provide intimate contact between the spaced tissue coagulationelectrodes (or other diagnostic or therapeutic elements) and the tissue.

[0011] Mapping baskets, which may be carried on the distal end ofseparate mapping catheters, are often used to locate the reentrypathways prior to the formation of lesions. Exemplary mapping basketsare disclosed in U.S. Pat. No. 5,823,189. Additionally, once the lesionshave been formed, the mapping baskets are again used to determinewhether the lesions have successfully eliminated the reentry pathways.Mapping baskets are superior to conventional diagnostic cathetersbecause mapping baskets do not need to be steered to a variety of siteswithin a bodily region such as the pulmonary vein during a diagnosticprocedure and, instead, can perform a diagnostic procedure in a singlebeat from a single location.

[0012] The use of a mapping catheter in combination with a soft tissuecoagulation catheter can, however, be problematic. For example, when amapping catheter is used in combination a soft tissue coagulationcatheter, a pair of transseptal punctures (or a single relatively largepuncture) must be formed in the atrial septum so that the catheters canbe advanced from the right atria, through the fossa ovalis and into theleft atria. Two punctures (or a relatively large single puncture) mustalso be formed in the femoral vein. In addition, the time required tomanipulate two catheters into their respective positions can lead toprolonged periods of fluoroscopy.

[0013] The issues associated with the combined use of mapping andcoagulation catheters notwithstanding, one lesion that has proven to bedifficult to form with conventional catheters is the circumferentiallesion that is used to isolate the pulmonary vein and cure ectopicatrial fibrillation. Lesions that isolate the pulmonary vein may beformed within the pulmonary vein itself or in the tissue surrounding thepulmonary vein. Conventional steerable catheters and loop catheters haveproven to be less than effective with respect to the formation of suchcircumferential lesions. Specifically, it is difficult to form aneffective circumferential lesion by forming a pattern of relativelysmall diameter lesions.

[0014] Accordingly, the inventors herein have determined that a needexists for a device that is capable of both mapping and coagulatingtissue. The inventors herein have further determined that a need existsgenerally for structures that can be used to create circumferentiallesions within or around bodily orifices. The inventors herein have alsodetermined that a need exists for a device that can both map thepulmonary vein and create lesions within or around the pulmonary vein.

SUMMARY OF THE INVENTION

[0015] Accordingly, the general object of the present inventions is toprovide a device that avoids, for practical purposes, the aforementionedproblems. In particular, one object of the present inventions is toprovide a device that can be used to create circumferential lesions inor around the pulmonary vein and other bodily orifices in a moreefficient manner than conventional apparatus. Another object of thepresent invention is to provide a device that can be used to both mapthe pulmonary vein and create lesions within or around the pulmonaryvein.

[0016] In order to accomplish some of these and other objectives, aprobe in accordance with one embodiment of a present invention includesa support body, an expandable/collapsible tissue coagulation structuresupported on the support body, and a mapping structure. The mappingstructure may be supported on the support body distally of theexpandable/collapsible tissue coagulation structure or, alternatively,passable through a lumen in the support body so that it can be advancedbeyond the distal end of the support body. Such a probe provides anumber of advantages over conventional apparatus. For example, thecombination of the tissue coagulation structure and the mappingstructure allows the physician to perform a mapping and coagulationprocedure with a single instrument, thereby eliminating theaforementioned problems in the art. The mapping structure may also bepositioned within the pulmonary vein or other orifice during acoagulation procedure and serve as an anchor to improve the accuracy ofthe placement of the coagulation structure. Additionally, the expandabletissue coagulation structure is especially useful for creating circularlesions in and around the pulmonary vein and other body orifices.

[0017] In order to accomplish some of these and other objectives, aprobe in accordance with one embodiment of a present invention includesa support body defining a longitudinal axis, an expandable/collapsiblehoop structure defining an open interior region and supported on thesupport body, at least one operative element supported on theexpandable/collapsible hoop structure. Such a probe provides a number ofadvantages over conventional apparatus. For example, in animplementation where the operative element consists of a plurality ofspaced electrodes, the hoop structure can be readily positioned suchthat the electrodes are brought into contact with tissue in or aroundthe pulmonary vein or other bodily orifice. The hoop structure alsodefines an open region that allows blood or other bodily fluids to passtherethrough. As a result, the present probe facilitates the formationof a circumferential lesion without the difficulties associated withconventional apparatus and does so without the occlusion of blood orother fluids.

[0018] The above described and many other features and attendantadvantages of the present inventions will become apparent as theinventions become better understood by reference to the followingdetailed description when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Detailed description of preferred embodiments of the inventionswill be made with reference to the accompanying drawings.

[0020]FIG. 1 is a side cutaway view of a probe in accordance with apreferred embodiment of a present invention.

[0021]FIG. 2 is a section view taken along line 2-2 in FIG. 1.

[0022]FIG. 3 is a side view of the probe illustrated in FIG. 1 incombination with a probe that supports a mapping basket.

[0023]FIG. 3a is a side view of a probe similar to the probe illustratedin FIG. 1 with an integral mapping basket.

[0024]FIG. 4 is a side view of a probe in accordance with a preferredembodiment of a present invention.

[0025]FIG. 5 is a cutaway view of a portion of the probe illustrated inFIG. 4.

[0026]FIG. 6 is a side view of a porous electrode illustrated in FIG. 4with fold lines added thereto.

[0027]FIG. 6a is a side view of a probe similar to the probe illustratedin FIG. 4 with the mapping basket mounted on a separate probe.

[0028]FIG. 7 is a side view of a probe in accordance with a preferredembodiment of a present invention.

[0029]FIG. 8 is a partial side view of the probe illustrated in FIG. 7in a collapsed orientation.

[0030]FIG. 9 is a partial perspective view of a portion of the probeillustrated in FIG. 7.

[0031]FIG. 10 is a side, partial section view of the probe handleillustrated in FIG. 7.

[0032]FIG. 11 is a side view of the probe illustrated in FIG. 7 incombination with a probe that supports a mapping basket.

[0033]FIG. 11a is a side view of a probe similar to the probeillustrated in FIG. 7 with an integral mapping basket.

[0034]FIG. 12 is a side view of a probe in accordance with a preferredembodiment of a present invention.

[0035]FIG. 13 is a partial perspective view of a portion of the probeillustrated in FIG. 12.

[0036]FIG. 14 is a side view of the probe illustrated in FIG. 12 in acollapsed orientation.

[0037]FIG. 14a is a side view of the probe illustrated in FIG. 12 incombination with a probe that supports a mapping basket.

[0038]FIG. 14b is a side view of a probe similar to the probeillustrated in FIG. 12 with an integral mapping basket.

[0039]FIG. 15 is a side view of a probe in accordance with a preferredembodiment of a present invention.

[0040]FIG. 16 is a perspective view of a probe in accordance with apreferred embodiment of a present invention.

[0041]FIG. 17 is an exploded perspective view showing certain elementsin the probe illustrated in FIG. 16.

[0042]FIG. 18 is perspective view of one of the structural members thatforms the hoop structure illustrated in FIGS. 16 and 17.

[0043]FIG. 19 is a perspective view of a probe in accordance with apreferred embodiment of a present invention.

[0044]FIG. 20 is a perspective view of a probe in accordance with apreferred embodiment of a present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] The following is a detailed description of the best presentlyknown modes of carrying out the inventions. This description is not tobe taken in a limiting sense, but is made merely for the purpose ofillustrating the general principles of the inventions.

[0046] The detailed description of the preferred embodiments isorganized as follows:

[0047] I. Introduction

[0048] II. Inflatable Structures

[0049] III. Hoop Structures

[0050] IV. Hoop Structure Electrodes, Temperature Sensing and PowerControl

[0051] The section titles and overall organization of the presentdetailed description are for the purpose of convenience only and are notintended to limit the present inventions.

[0052] I. Introduction

[0053] The present inventions may be used within body lumens, chambersor cavities for diagnostic or therapeutic purposes in those instancewhere access to interior bodily regions is obtained through, forexample, the vascular system or alimentary canal and without complexinvasive surgical procedures. For example, the inventions herein haveapplication in the diagnosis and treatment of arrhythmia conditionswithin the heart. The inventions herein also have application in thediagnosis or treatment of ailments of the gastrointestinal tract,prostrate, brain, gall bladder, uterus, and other regions of the body.

[0054] With regard to the treatment of conditions within the heart, thepresent inventions are designed to produce intimate tissue contact withtarget substrates associated with various arrhythmias, namely atrialfibrillation, atrial flutter, and ventricular tachycardia. For example,the distal portion of a catheter in accordance with a present invention,which may include diagnostic and/or soft tissue coagulation electrodes,can be used to create lesions within or around the pulmonary vein totreat ectopic atrial fibrillation.

[0055] The structures are also adaptable for use with probes other thancatheter-based probes. For example, the structures disclosed herein maybe used in conjunction with hand held surgical devices (or “surgicalprobes”). The distal end of a surgical probe may be placed directly incontact with the targeted tissue area by a physician during a surgicalprocedure, such as open heart surgery. Here, access may be obtained byway of a thoracotomy, median sternotomy, or thoracostomy. Exemplarysurgical probes are disclosed in co-pending U.S. application Ser. No.09/072,872, filed May 5, 1998, and entitled “Surgical Methods andApparatus for Positioning a Diagnostic or Therapeutic Element Within theBody.”

[0056] Surgical probe devices in accordance with the present inventionspreferably include a handle, a relatively short shaft, and one of thedistal assemblies described hereafter in the catheter context.Preferably, the length of the shaft is about 4 inches to about 18inches. This is relatively short in comparison to the portion of acatheter body that is inserted into the patient (typically from 23 to 55inches in length) and the additional body portion that remains outsidethe patient. The shaft is also relatively stiff. In other words, theshaft is either rigid, malleable, or somewhat flexible. A rigid shaftcannot be bent. A malleable shaft is a shaft that can be readily bent bythe physician to a desired shape, without springing back when released,so that it will remain in that shape during the surgical procedure.Thus, the stiffness of a malleable shaft must be low enough to allow theshaft to be bent, but high enough to resist bending when the forcesassociated with a surgical procedure are applied to the shaft. Asomewhat flexible shaft will bend and spring back when released.However, the force required to bend the shaft must be substantial.

[0057] II. Inflatable Structures

[0058] As illustrated for example in FIGS. 1 and 2, a catheter 10 inaccordance with a preferred embodiment of a present invention includes aflexible catheter body 12 that may be formed from a biocompatiblethermoplastic material such as braided or unbraided Pebax® (polyetherblock emide), polyethylene, or polyurethane, and is preferably about 5French to about 9 French in diameter. Preferably, the catheter body 12will have a two part construction consisting of a relatively shortflexible distal member (formed from unbraided Pebax®) and a longer lessflexible proximal member (formed from braided Pebax®). The proximal anddistal members may be bonded together with an overlapping thermal bondor adhesive bonded together end to end over a sleeve in what is referredto as a “butt bond.” The proximal end of the catheter body 12 is securedto a handle 14. An expandable (and collapsible) coagulation body 16 ismounted near the distal end of the catheter body 12. As described below,the expandable coagulation body 16 may be heated to a temperature thatwill cause soft tissue in contact with the coagulation body tocoagulate.

[0059] The expandable coagulation body 16, which is bonded to anddisposed around the catheter body 12, can be inflated with water,hypertonic saline solution, or other biocompatible fluids. The fluid issupplied under pressure to the catheter 10 through aninfusion/ventilation port 18. The pressurized fluid travels to and fromthe expandable coagulation body 16 through a fluid lumen 20 in thecatheter body 12 and an aperture 22 located within the expandablecoagulation body. Pressure is maintained to maintain the expandablecoagulation body 16 in the expanded orientation illustrated in FIG. 1.The pressure should be relatively low (less than 5 psi) and will vary inaccordance with the desired level of inflation, strength of materialsused and the desired degree of body flexibility. The fluid may beremoved from the expandable coagulation body 16 by applying a suctionforce to the infusion/ventilation port 18.

[0060] For applications associated with the creation of lesions in oraround the pulmonary vein, the exemplary expandable coagulation body 16is preferably located about 3 cm to about 5 cm from the distal tip ofthe catheter body 12 and the diameter is between about 2 mm and about 6mm in the collapsed state and between about 10 mm and about 30 mm in theexpanded (or inflated) state. Suitable materials for the expandablecoagulation body 16 include relatively elastic thermally conductivebiocompatible materials such as silicone and polyisoprene. Other lesselastic materials, such as Nylon®, Pebax®, polyethylene and polyester,may also be used. Here, the expandable coagulation body will have to beformed with fold lines. [Note the discussion below concerning fold lineswith respect to the exemplary embodiment illustrated in FIG. 6.]Additionally, although the exemplary expandable coagulation body 16 hasa spherical shape, other shapes, such as a tear drop shape, acylindrical shape, or a prolate ellipsoid, may also be employed.

[0061] A fluid heating element is located within the expandablecoagulation body 16. In the preferred embodiment illustrated in FIGS. 1and 2, the fluid heating element is an electrode 24 that is mounted onthe catheter body 12. Alternatively, a bi-polar pair of electrodes maybe used to transmit power through a conductive fluid, such as theaforementioned isotonic saline solution, to generate heat. Thetemperature of the fluid may be heated to about 90° C., thereby raisingthe temperature of the exterior of the expandable coagulation body 16 toapproximately the same temperature for tissue coagulation. The electrodemay be formed from metals such as platinum, gold and stainless steel.

[0062] The expandable coagulation body 16 tends to produce relativelysuperficial lesions. As such, it is especially useful for creatinglesions within the pulmonary vein.

[0063] The temperature of the fluid is preferably monitored for powercontrol purposes. To that end, a temperature sensing element, such asthe illustrated thermocouple 26, may mounted on the catheter body 12within the expandable coagulation body 16. A reference thermocouple 28may be positioned near the distal end of the catheter body 12.Alternatively, a thermistor or other temperature sensing element may beused in place of the thermocouple and reference thermocouplearrangement. The electrode 24, thermocouple 26 and referencethermocouple 28 are respectively connected to an electrical connector 30by electrical conductors 32, 34 and 36 which extend through a conductorlumen 38 in the catheter body. The connector 30 may be connected to asuitable RF power supply and control apparatus.

[0064] The exemplary catheter body 12 illustrated in FIGS. 1 and 2 alsoincludes a central lumen 40 that is associated with a central port 42.The purpose of the central lumen is essentially two-fold. The centrallumen 40 serves as a guidewire lumen when the probe 10 is being directedto a bodily region of interest such as the pulmonary vein. A guidewire44 is first directed into the bodily region in conventional fashion andthe probe 10 is then advanced over the guidewire. A relatively shortintroducer sheath may be used to facilitate insertion of the catheter 10into the vasculature. Alternatively, a sheath which extends to theanatomical region of interest may be used. Once the probe reaches thebodily region of interest, the guidewire 44 may be removed so that thelumen can be used for its other purpose, which is to provide a passageto the bodily region for another device.

[0065] As illustrated for example in FIG. 3, a conventional basketcatheter 46, such as the Constellation® basket catheter manufactured byEP Technologies, Inc. in San Jose, Calif., may be advanced through thecentral lumen 40. The exemplary basket catheter 46 includes an elongatecatheter body 48, a mapping and/or coagulation basket 50 and ahandle/electrical connector 52. The basket may include two to eightelectrode supporting splines 54 and one to eight electrodes 56 on eachspline. The splines 54, which are preferably made of a resilient,biologically inert material such as Nitinol® metal, stainless steel orsilicone rubber, may be arranged either symmetrically or asymmetricallyabout the longitudinal axis of the basket 50. The splines 54 areconnected between a base member 58 and an end cap 60 in a resilient,pretensed, radially expanded condition, to bend and conform to theendocardial tissue surface they contact.

[0066] The exemplary basket 50 illustrated in FIG. 3, which is intendedto be inserted into the pulmonary vein for pacing and mapping thereof,includes four splines 54 that respectively support two electrodes 56.The basket 50 also has a substantially elliptical shape and is betweenabout 20 mm and about 40 mm in diameter in its expanded state and about5 cm in length. Additional details concerning basket structures aredisclosed in U.S. Pat. No. 5,823,189, which is incorporated herein byreference.

[0067] The combination of the exemplary catheter 10 and basket catheter46 allows the physician to perform mapping and coagulation procedurewith a single instrument, thereby eliminating the aforementionedproblems in the art. Moreover, the basket 50 may be positioned withinthe pulmonary vein or other orifice during a coagulation procedure andserve as an anchor to improve the accuracy of the placement of theexpandable coagulation body 16. In those instances where the basket isnot present, the distal portion of the catheter body can serve as theanchor.

[0068] Another exemplary catheter in accordance a present invention isillustrated in FIGS. 4-6 and generally represented by reference numeral62. Catheter 62 is in many ways similar to the catheter illustrated inFIGS. 1-3 and like elements are represented with the like referencenumerals. There are, however, two primary differences. Catheter 62includes an expandable (and collapsible) porous electrode structure 64,as opposed to the heated expandable coagulation body 16, and theelectrode supporting basket 50 is mounted on the distal portion of thecatheter body 12, as opposed to being mounted on a separate catheterthat is advanced through the central lumen 40.

[0069] As shown by way of example in FIG. 5, the expandable porouselectrode 64, which is formed from an electrically non-conductivethermoplastic or elastomeric material, includes a porous region 66having pores 68 and two non-porous regions 70 and 72. The pores 68,which are actually micropores, are shown diagrammatically in enlargedform for the purpose of illustration. Liquid pressure is used to inflatethe expandable porous electrode 64 and maintain it in its expandedstate. The liquid, which is supplied through the infusion/ventilationport 18 and fluid lumen 20 (FIG. 2), enters the expandable porouselectrode 64 by way of the aperture 22. The expandable porous electrode64 will then expand from its collapsed, low profile state (between about2.3 mm and about 5.3 mm in diameter) to its expanded state (betweenabout 10 mm and about 30 mm).

[0070] An electrode 24 formed from material with both relatively highelectrical conductivity and relatively high thermal conductivity iscarried within the expandable porous electrode 64. Suitable materialsinclude gold, platinum, and platinum/iridium. Noble metals arepreferred. Here too, the electrode 24, thermocouple 26 and referencethermocouple 28 are connected to the electrical connector 30 byelectrical conductors 32, 34 and 36 which extend through conductor lumen38 in the catheter body 12 (note FIG. 2). The liquid used to fill theexpandable porous electrode 64 is an electrically conductive liquid thatestablishes an electrically conductive path to convey RF energy from theelectrode 24 to tissue.

[0071] The pores 68 establish ionic transport of the tissue coagulatingenergy from the electrode 24 through the electrically conductive fluidto tissue outside the porous electrode 64. The liquid preferablypossesses a low resistivity to decrease ohmic loses, and thus ohmicheating effects, within the porous electrode 64. The composition of theelectrically conductive liquid can vary. A hypertonic saline solution,having a sodium chloride concentration at or near saturation, which isabout 20% weight by volume is preferred. Hypertonic saline solution hasa low resistivity of only about 5 ohm·cm, compared to blood resistivityof about 150 ohm·cm and myocardial tissue resistivity of about 500ohm·cm. Alternatively, the fluid can be a hypertonic potassium chloridesolution. This medium, while promoting the desired ionic transfer,requires closer monitoring of the rate at which ionic transport occursthrough the pores 68, to prevent potassium overload. When hypertonicpotassium chloride solution is used, it is preferred keep the ionictransport rate below about 1 mEq/min.

[0072] Ionic contrast solution, which has an inherently low resistivity,can be mixed with the hypertonic sodium or potassium chloride solution.The mixture enables radiographic identification of the porous electrode64 without diminishing the ionic transfer through the pores 68.

[0073] Due largely to mass concentration differentials across the pores68, ions in the conductive fluid will pass into the pores because ofconcentration differential-driven diffusion. Ion diffusion through thepores 68 will continue as long as a concentration gradient is maintainedacross the porous electrode 64. The ions contained in the pores 68provide the means to conduct current across the porous electrode 64.When RF energy is conveyed from a RF power supply and control apparatusto the electrode 24, electric current is carried by the ions within thepores 68. The RF currents provided by the ions result in no netdiffusion of ions, as would occur if a DC voltage were applied, althoughthe ions do move slightly back and forth during the RF frequencyapplication. This ionic movement (and current flow) in response to theapplied RF field does not require perfusion of liquid through the pores68. The ions convey RF energy through the pores 68 into tissue to areturn electrode, which is typically an external patch electrode(forming a unipolar arrangement). Alternatively, the transmitted energycan pass through tissue to an adjacent electrode (forming a bipolararrangement). The RF energy heats tissue (mostly ohmically) to coagulatethe tissue and form a lesion.

[0074] The preferred geometry of the expandable porous electrode 64 isessentially tear drop-shaped and symmetric with a ring of pores 68surrounded by non-porous regions. The ring is preferably about 2 mm toabout 10 mm wide. This porous electrode configuration is especiallyuseful for forming relatively deep lesions around the entrance to thepulmonary vein. However, nonsymmetrical or non tear drop-shapedgeometries can be used. The porous electrode may, for example, be formedwith a spherical shape. Elongated, cylindrical geometries can also beused. The distal non-porous region 72 may be eliminated and replacedwith a porous region. The shape and size of the porous region 66 mayalso be varied.

[0075] With respect to materials, the porous region 66 of the expandableporous electrode 64 is preferably formed from regenerated cellulose or amicroporous elastic polymer. Hydroscopic materials with microporescreated through the use of lasers, electrostatic discharge, ion beambombardment or other processes may also be used. The non-porous regionsare preferably formed from relatively elastic materials such as siliconeand polyisoprene. However, other less elastic materials, such as Nylon®,Pebax®, polyethylene, polyesterurethane and polyester, may also be used.Here, the expandable porous electrode 64 may be provided with creasedregions 74 that facilitate the collapse of the porous electrode, as isillustrated for example in FIG. 6. A hydrophilic coating may be appliedto the non-porous regions to facilitate movement of the porous electrode64 in to and out of a sheath.

[0076] Like the exemplary catheter 10 illustrated in FIGS. 1-3,exemplary catheter 62 may be directed to the anatomical site ofinterest, such as the pulmonary vein, by advancing the catheter througha relatively short introducer sheath and over a guidewire 44. However,because the basket 50 is mounted on the distal end of the catheter, thebase member 58 and end cap 60 are provided with apertures through whichthe guidewire 44 extends. A relatively short introducer sheath may beused to facilitate insertion of the catheter 62 into the vasculature or,alternatively, a sheath which extends to the anatomical region ofinterest may be used.

[0077] It should be noted that the exemplary catheter 10 illustrated inFIGS. 1-3 may be provided with a basket that is fixedly mounted on thedistal end of the catheter body 12. Such a catheter is identified byreference numeral 10′ in FIG. 3a. Similarly, the basket may be removedfrom the catheter 62 illustrated in FIGS. 4-6 so that a separate basketcatheter may be used in combination therewith in a manner similar tothat illustrated in FIG. 3. Such a catheter is identified by referencenumeral 46′ in FIG. 6a.

[0078] Additional information and examples of expandable and collapsiblebodies are disclosed in U.S. patent application Ser. No. 08/984,414,entitled “Devices and Methods for Creating Lesions in Endocardial andSurrounding Tissue to Isolate Arrhythmia Substrates,” U.S. Pat. No.5,368,591, and U.S. Pat. No. 5,961,513, each of which is incorporatedherein by reference.

[0079] III. Hoop Structures

[0080] As illustrated for example in FIGS. 7-10, a catheter 76 inaccordance with an invention herein includes a catheter body 78 thatsupports a collapsible hoop structure 80 at or near its distal end. Thehoop structure 80 may be used to support one or more operative elementsin contact with an annular tissue region such as the pulmonary vein. Forexample, the hoop structure 80 may be used to support a plurality ofspaced electrodes 82. The exemplary collapsible hoop structure 80includes a substantially circular hoop spline 84, a pair of distalsupport splines 86 and a pair of proximal support splines 88. The shapeof the hoop spline 84 may, alternatively, be oval, elliptical or anyother two or three-dimensional shape required for a particularapplication. The end of each of the support splines 86 and 88 includes aloop 89 that encircles the corresponding portion of the hoop spline 84in the manner illustrated in FIG. 9. Excessive movement of the supportsplines 86 and 88 around the circumference of the hoop spline 84 isprevented by the electrodes 82.

[0081] The exemplary collapsible hoop structure 80 may be driven fromthe expanded orientation illustrated in FIG. 7 to the collapsedorientation illustrated in FIG. 8 by moving the distal support splines86 and proximal support splines 88 away from one another. In theillustrated embodiment, the catheter body 78 is configured to move theproximal and distal support splines 86 and 88 in this manner. Morespecifically, the catheter body 78 includes a pair of catheter bodymembers 90 and 92 that are movable relative to one another. The catheterbody members 90 and 92 are preferably tubular members arranged such thatmember 92 is slidably received within the lumen of member 90. The distalsupport splines 86 are secured to the catheter body member 90, while theproximal support splines 88 are secured to the catheter body member 92.When the catheter body member 92 is moved proximally relative to thecatheter body member 90, the distal and proximal support splines 86 and88 will be moved away from one another to collapse the hoop structure80. Relative movement in the opposite direction will expand the supportstructure. Of course, the catheter body member 92 may be moved relativeto the catheter body member 90, or both catheter body members may bemoved, in other implementations of the invention.

[0082] In the exemplary embodiment illustrated in FIGS. 7-10, the distaland proximal support splines 86 and 88 are secured to the catheter bodymembers 90 and 92 with anchor rings 94 and 96. The distal and proximalsupport splines 86 and 88 are preferably spot welded to the anchor rings94 and 96 and the anchor rings are preferably glued to the catheter bodymembers 90 and 92. Other methods of attachment may also be used.

[0083] The hoop spline 84, distal support splines 86 and proximalsupport splines 88 are preferably made of a resilient, biologicallyinert material such as Nitinol® metal, stainless steel or an elasticpolymer (e.g. silicone rubber). The splines are preshaped into theconfigurations corresponding to an expanded hoop structure 80. In animplementation suitable for pulmonary vein applications, the hoop spline84 will be about 10 mm to about 30 mm in diameter. The catheter bodymembers 90 and 92 may be formed from a biocompatible thermoplasticmaterial such as braided or unbraided Pebax®, polyethylene, orpolyurethane. In an implementation suitable for pulmonary veinapplications, the catheter body member 90 will have an outer diameter ofabout 1.5 mm and an inner diameter of about 1 mm, while the catheterbody member 92 will have an outer diameter of about 2.2 mm and an innerdiameter of about 1.6 mm.

[0084] The splines are preferably covered with tubes formed from abiocompatible polymer material such as Pebax® or Nylon®. Conductor wires(not shown) for the electrodes 82 and temperature sensors 83 (discussedin Section IV below) pass through the tubes and into the lumen of thecatheter body member 90.

[0085] The exemplary catheter 76 also includes a handle 98 capable ofmoving the catheter body members 90 and 92 relative to one another.Referring more specifically to FIG. 10, the exemplary handle 98 includesa handle body 100 with a suitable electrical connector (not shown) forthe conductor wires from the electrodes 82 and temperature sensors 83, apiston 102 that is slidably mounted in a longitudinally extendingaperture in the handle body, and a thumb rest 104. The handle body 100,piston 102 and thumb rest 104 are preferably formed from machined ormolded plastic. The catheter body member 92 is secured to a strainrelief element 105 on the thumb rest 104 with an adhesive or othersuitable instrumentality. The catheter body member 90 extends throughthe catheter body member 92, through a lumen formed in the piston 102and into the proximal portion of the handle body 100. The catheter bodymember 90 is glued or otherwise secured to an anchor 106 which is itselfheld in place by a set screw 108 or other suitable device. As theposition of the catheter body member 90 is fixed relative to the handle100 and the piston 102 and proximal catheter body member 92 are notfixed relative to the handle, the catheter body member 92 may be movedrelative to the catheter body member 90 by moving the piston.

[0086] In order to insure that the piston 102 in the exemplary handle 98illustrated in FIGS. 7, 8 and 10 does not move once it has been placedin the position corresponding to a collapsed hoop structure 80, a setscrew 110 engages a key way 112 formed in the piston. The friction forcebetween the set screw 110 and key way 112 is sufficient to overcome theforce generated by a collapsed hoop structure 80. Additionally, thelongitudinal edges of the piston key way 112 limit the range of motionof the piston 102 by engaging the set screw 110. In the preferredembodiment, the length of the key way 112 is approximately 0.75 inch,but can range from approximately 0.375 inch to approximately 1.5 inches.Additionally, although the preferred embodiment includes theabove-described set screw and key way arrangement, other mechanisms forapplying a friction force to the piston and limiting its range of motionmay also be employed. For example, fluting to limit the range of pistonmotion, a tapered collet, o-rings in addition to those discussed below,or a circumferential piston grip may be used in place of the preferredscrew and key way arrangement.

[0087] The exemplary handle 98 also includes a compression spring 114that applies a distally directed biasing force to the piston 102. Thebiasing force reduces the amount of force that must be applied to thepiston 102 by the physician to move the piston in the distal directionand expand the hoop structure 80. The compression spring 114 is locatedbetween the proximal end of the piston 102 and an annularly shapedabutment 116. Because of the biasing force imparted to the piston 102 bythe compression spring 114, the amount of physician-generated actuationforce required to drive the piston is reduced.

[0088] A pair of o-rings 118 may be used to center the piston 102 withinthe handle body 100 of the exemplary handle 98. The o-rings 118 alsoprevent the piston from canting. The side of the exemplary piston 102opposite the key way 112 includes a pair of Teflon® rods 120 which rideon the surface of the longitudinally extending aperture in the handlebody 100. The Teflon® rods 120 provide improved lubricity and preventthe set screw 110 from driving the piston 102 into the surface of theaperture.

[0089] The exemplary catheter 76 may be advanced over a guidewire 122(located within the inner lumen of the catheter body member 90) into thebodily region of interest in conventional fashion. A relatively shortintroducer sheath or a sheath which extends to the anatomical region ofinterest may be used if desired. The hoop structure 80 can then beexpanded and used to create an annular lesion at the entrance to orwithin, for example, the pulmonary vein. Additionally, because theelectrodes 82 or other operative elements are mounted on a hoop spline84, tissue coagulation can be achieved without occluding blood flow.

[0090] The inner lumen of the catheter body member 90 may also be usedto provide a passage to the bodily region for another device. Asillustrated for example in FIG. 11, a conventional basket catheter 124,such as the Constellation® basket catheter manufactured by EPTechnologies, Inc. in San Jose, Calif., may be advanced through thelumen of the distal catheter member 90. The basket catheter 124 may beadvanced over the guidewire 122, as shown, or the guidewire may beremoved from the lumen in the catheter body member prior to insertion ofthe basket catheter.

[0091] The exemplary basket catheter 124 includes an elongate catheterbody 126, a mapping and/or coagulation basket 128 and ahandle/electrical connector (not shown). Like the basket 50 describedabove with reference to FIG. 3, the exemplary basket 128 includes foursymmetrically arranged splines 129, which are preferably made of aresilient, biologically inert material such as Nitinol® metal, stainlesssteel or silicone rubber. Each spline 129 supports two electrodes 130and is supported in a resilient, pretensed, radially expanded conditionbetween a base member 132 and an end cap 134. Basket catheter 124 isconfigured for use within the pulmonary vein and has a substantiallyelliptical shape and is between about 20 mm and about 40 mm in diameterin its expanded state and about 5 cm in length in the collapsed state.Nevertheless, the number of splines and electrodes on each spline, aswell as the overall size of the basket 128, may be increased ordecreased as applications require.

[0092] The combined catheter 76 and basket catheter 124 allows thephysician to perform mapping and coagulation procedure with a singleinstrument, thereby eliminating the aforementioned problems in the art.The basket can also be used as an anchor to improve the accuracy of theplacement of the hoop structure 80.

[0093] As illustrated for example in FIG. 11a, a catheter 76′, which isotherwise identical to catheter 76, may include a basket 128′ that isintegral with distal end of the catheter body member 90. Here, thehandle 100 would also include a suitable electrical connector for thebasket 128′.

[0094] Another exemplary catheter including a collapsible hoopstructure, which is generally represented by reference numeral 136, isillustrated in FIGS. 12-14. The catheter includes a catheter body 138that supports a collapsible hoop structure 140. The hoop structure 140may be used to support one or more operative elements in contact with anannular tissue region such as the pulmonary vein. For example, the hoopstructure 140 may be used to support a plurality of spaced electrodes142. The exemplary hoop structure 140 includes a substantially circularhoop spline 144 and four radially extending support splines 146. Theshape of the hoop spline 144 may, alternatively, be oval, elliptical orany other shape required for a particular application. The supportsplines 146 are welded or otherwise secured to an anchor ring 147 thatis mounted on the catheter body 138. The anchor ring 147 may be held inplace with an interference fit, adhesive, or a combination thereof.

[0095] A first pair of stylets 148 a and 148 b and a second pair ofstylets 150 a and 150 b are attached to the exemplary hoop spline 144.The ends support splines 146 and stylets 148 a, 148 b, 150 a and 150 binclude respective loops 152 that encircle the corresponding portion ofthe hoop spline 144 in the manner illustrated in FIG. 13. The stylets148 a, 148 b and 150 a, 150 b extend into a lumen within the catheterbody 138 through apertures 154 and are wound into respective styletpairs 148 and 150.

[0096] The catheter body 138 and support splines 146 may be formed fromthe same materials as their counterparts in the preferred embodimentillustrated in FIGS. 7-11. In particular, the support splines 146 arepreferably formed from Nitinol® metal, stainless steel or an elasticpolymer, and the anchor ring 147 should be formed from the same materialas the support splines. The stylets 148 a, 148 b, 150 a and 150 b may beformed from inert wire such as Nitinol® or 17-7 stainless steel wire.The catheter body also includes lumens for the stylets, electricalconductors associated with the electrodes and temperature sensors, and aguidewire.

[0097] The exemplary catheter 136 also includes a handle 156. The woundstylet pairs 148 and 150 pass through handle apertures 158 and 160 andthe proximal ends of the stylet pairs may be provided with grips 162 and164. The exemplary hoop structure 140 may be driven from the expandedorientation illustrated in FIG. 12 to the collapsed orientationillustrated in FIG. 14 by moving the stylet pair 148 (and stylets 148 aand 148 b) in the distal direction and moving the stylet pair 150 (andstylets 150 a and 150 b) in the proximal direction. Alternatively, thehandle may be provided with conventional bi-directional steeringapparatus, such as the rotatable knob arrangement illustrated in U.S.Pat. No. 5,254,088 or the rotatable gear and rack arrangementillustrated in U.S. Pat. No. 5,364,351, to drive the stylet pairs 148and 150 in opposite directions. In any event, the handle 156 preferablyalso includes an electrical connector 166.

[0098] The exemplary catheter 136 may be advanced over a guidewire thatpasses through a lumen in the catheter body member 138. A relativelyshort introducer sheath or a sheath which extends to the anatomicalregion of interest may be used if desired. Here too, the hoop structure140 can then be expanded and used to create an annular lesion withoutoccluding blood flow.

[0099] The exemplary catheter illustrated in FIGS. 12-14 may also beused in conjunction with a mapping basket. As illustrated for example inFIG. 14a, a basket catheter 124 such as that illustrated in FIG. 11 maybe advanced through the guidewire lumen of catheter 136. Alternatively,as illustrated for example in FIG. 14b, a modified catheter 136′includes a basket 128′ mounted on the distal end of the catheter body138.

[0100] Other types of lesion creating catheters may be provided with anintegral mapping basket. As illustrated for example in FIG. 15,exemplary catheter 168 includes a proximal portion 170, a helical distalportion 172 and an integral mapping/coagulation basket 174. The helicaldistal portion 172 preferably supports a plurality of electrodes 176.The number of revolutions, length, diameter and shape of the helicalportion 172 will vary from application to application. The helicalportion illustrated in FIG. 15, which may be used to create lesions inor around the pulmonary vein, revolves around the longitudinal axis ofthe catheter 168 one and one-half times in its relaxed state. The basket174, which is essentially the same as those described above, includesfour splines 178 and a pair of electrodes 180 on each spline. Otherbasket configurations may be used as applications so require.

[0101] The exemplary catheter 168 also includes a stylet 182 thatenables the physician to manipulate the helical distal portion 172 andadjust its shape. The distal portion of the stylet 182 is fixedlysecured within the region of the catheter distal of the helical distalportion 172. The stylet 182 can be moved distally and proximally and canalso be rotated in one direction, which will cause the helical portionof unwind so that its diameter decreases, or rotated in the otherdirection to cause its diameter to decrease. In any of these states, thehelical portion will define an open area interior to the electrodes 176through which blood or other bodily fluids can flow. As a result, thehelical portion can be used to create a circumferential lesion in oraround the pulmonary vein, or other bodily orifice, without occludingfluid flow.

[0102] The exemplary catheter 168 illustrated in FIG. 15 is not asteerable catheter and, accordingly, may be advanced though aconventional steerable guide sheath to the target location. The sheathshould be lubricious to reduce friction during movement of the catheter168. Prior to advancing the catheter 168 into the sheath, the stylet 182will be moved to and held in its distal most position in order tostraighten out the helical distal portion 172. The stylet 182 willremain in this position until the helical distal portion 172 is advancedbeyond the distal end of the sheath. A sheath introducer, such as thoseused in combination with basket catheters, may be used when introducingthe catheter into the sheath.

[0103] Additional information concerning the helical catheterillustrated in FIG. 15, albeit without the mapping basket, is disclosedin concurrently filed and commonly assigned U.S. application Ser. No.______, which is entitled “Loop Structures For Supporting Diagnostic andTherapeutic Elements in Contact With Body Tissue” and incorporatedherein by reference.

[0104] Another exemplary catheter with a hoop structure is illustratedin FIGS. 16-18. Referring first to FIG. 16, the catheter 184 includes acatheter body 186 and a collapsible hoop structure 188 at the distal endthereof. The hoop structure 188 may be used to support one or moreoperative elements, such as the illustrated electrodes 190, in contactwith an annular tissue region such as the pulmonary vein. The exemplaryhoop structure 188 includes a substantially circular hoop spline 192 andfour support splines 194. The hoop spline 192 may also be oval,elliptical or any other shape, and the number of support splines 194 maybe increased or decreased, as applications require. In an implementationsuitable for pulmonary vein applications, the hoop spline 192 will beabout 10 mm to about 30 mm in diameter.

[0105] As illustrated for example in FIGS. 17 and 18, the exemplary hoopstructure 188 is composed of four substantially identical structuralmembers 196, each of which consists of a pair of struts 198 and a curvedportion 200 that extends approximately ninety degrees, and four moldedtubes 202 that extend outwardly from the catheter body 186. One strut198 from each of two adjacent structural members 196 is inserted into atube 202. To that end, the struts 198 are formed with bends 204 so thatthe struts will conform to the shape of the region 206 that includes thedistal portion of the catheter body 186 and the tubes 202 that extendoutwardly therefrom. Each support spline 194 is, therefore, a compositestructure consisting of two struts 198 and a molded tube 202. Wiringfrom the electrodes 190 and temperature sensors associated with theelectrodes (not shown) will pass through the tubes 202 and into a lumenextending through the catheter body 186.

[0106] The structural members 196 are preferably formed from aresilient, biologically inert material such as Nitinol® metal, stainlesssteel or silicone rubber that is preshaped into the configurationcorresponding to an expanded hoop structure 188. The catheter body 186and molded tubes 202 may be formed from a biocompatible thermoplasticmaterial such as braided or unbraided Pebax®, polyethylene, orpolyurethane.

[0107] A relatively short introducer sheath and, preferably, a sheathwhich extends to the anatomical region of interest will be used inconjunction with the exemplary catheter illustrated in FIGS. 16-18. Heretoo, the hoop structure can be expanded and used to create an annularlesion at the entrance to or within, for example, the pulmonary veinwithout occluding blood flow.

[0108] As illustrated for example in FIG. 19, the exemplary hoopstructure 188 illustrated in FIGS. 16-18 can be reconfigured slightly inorder to increase the collapsibility of the structure. The exemplaryhoop structure 188′ is essentially identical to hoop structure 188 butfor the configuration of the structural members 196. Here, the curvedportions 200′ in hoop structure 188′ are rotated distally in thedirection of the arrows “A” relative to the curved portions 200 in hoopstructure 188 to increase the collapsibility.

[0109] Still another exemplary hoop structure is illustrated in FIG. 20and generally represented by reference numeral 208. Here, the catheteris provided with a catheter body 210 and a collapsible hoop structure212 at the distal end thereof. The hoop structure 212 may be used tosupport one or more operative elements, such as the illustratedelectrodes 214, in contact with an annular tissue region such as thepulmonary vein. The exemplary hoop structure 212 includes asubstantially circular hoop spline 216, four proximal support splines218, four distal support splines 220, a base 222 and an end cap 224. Inaddition to providing additional structural support, the distal supportsplines 220 act as an anchor during tissue coagulation procedures. Thehoop spline 214 will be about 10 mm to about 30 mm in diameter inimplementations suitable for pulmonary vein applications. The hoopspline 216 may also be oval, elliptical or any other shape, and thenumber of support splines 218, 220 may be increased or decreased, asapplications require.

[0110] IV. Hoop Structure Electrodes, Temperature Sensing and PowerControl

[0111] In each of the preferred embodiments, the operative elements area plurality of spaced electrodes. However, other operative elements,such as lumens for chemical ablation, laser arrays, ultrasonictransducers, microwave electrodes, and resistive heating wires, and suchdevices may be substituted for the electrodes. Additionally, althoughelectrodes and temperature sensors are discussed below in the context ofthe exemplary catheter described with reference to FIGS. 7-11, thediscussion is also applicable to the exemplary catheters described withreference to FIGS. 12-20.

[0112] The spaced electrodes 82 are preferably in the form of wound,spiral coils. The coils are made of electrically conducting material,like copper alloy, platinum, or stainless steel, or compositions such asdrawn-filled tubing (e.g. a copper core with a platinum jacket). Theelectrically conducting material of the coils can be further coated withplatinum-iridium or gold to improve its conduction properties andbiocompatibility. A preferred coil electrode is disclosed in U.S. Pat.No. 5,797,905. The electrodes 82 are electrically coupled to individualwires (such as those illustrated in FIG. 2) to conduct coagulatingenergy to them. The wires are passed in conventional fashion through alumen extending through the associated catheter body into a PC board inthe catheter handle, where they are electrically coupled to a connectorthat is received in a port on the handle. The connector plugs into asource of RF coagulation energy.

[0113] As an alternative, the electrodes may be in the form of solidrings of conductive material, like platinum, or can comprise aconductive material, like platinum-iridium or gold, coated upon thedevice using conventional coating techniques or an ion beam assisteddeposition (IBAD) process. For better adherence, an undercoating ofnickel or titanium can be applied. The electrodes can also be in theform of helical ribbons. The electrodes can also be formed with aconductive ink compound that is pad printed onto a nonconductive tubularbody. A preferred conductive ink compound is a silver-based flexibleadhesive conductive ink (polyurethane binder), however other metal-basedadhesive conductive inks such as platinum-based, gold-based,copper-based, etc., may also be used to form electrodes. Such inks aremore flexible than epoxy-based inks.

[0114] The flexible electrodes 82 are preferably about 4 mm to about 20mm in length. In the preferred embodiment, the electrodes are 12.5 mm inlength with 1 mm to 3 mm spacing, which will result in the creation ofcontinuous lesion patterns in tissue when coagulation energy is appliedsimultaneously to adjacent electrodes. For rigid electrodes, the lengthof the each electrode can vary from about 2 mm to about 10 mm. Usingmultiple rigid electrodes longer than about 10 mm each adversely effectsthe overall flexibility of the device, while electrodes having lengthsof less than about 2 mm do not consistently form the desired continuouslesion patterns.

[0115] The portion of the electrodes that are not intended to contacttissue (and be exposed to the blood pool) may be masked through avariety of techniques with a material that is preferably electricallyand thermally insulating. This prevents the transmission of coagulationenergy directly into the blood pool and directs the energy directlytoward and into the tissue. For example, a layer of UV adhesive (oranother adhesive) may be painted on preselected portions of theelectrodes to insulate the portions of the electrodes not intended tocontact tissue. Deposition techniques may also be implemented toposition a conductive surface only on those portions of the assemblyintended to contact tissue. Alternatively, a coating may be formed bydipping the electrodes in PTFE material.

[0116] The electrodes may be operated in a uni-polar mode, in which thesoft tissue coagulation energy emitted by the electrodes is returnedthrough an indifferent patch electrode (not shown) externally attachedto the skin of the patient. Alternatively, the electrodes may beoperated in a bi-polar mode, in which energy emitted by one or moreelectrodes is returned through other electrodes. The amount of powerrequired to coagulate tissue ranges from 5 to 150 w.

[0117] As illustrated for example in FIG. 9, a plurality of temperaturesensors 83, such as thermocouples or thermistors, may be located on,under, abutting the longitudinal end edges of, or in between, theelectrodes 82. Preferably, the temperature sensors 83 are located at thelongitudinal edges of the electrodes 82 on the distally facing side ofthe hoop or helical structure. In some embodiments, a referencethermocouple (not shown) may also be provided. For temperature controlpurposes, signals from the temperature sensors are transmitted to thesource of coagulation energy by way of wires (such as those illustratedin FIG. 2) that are also connected to the aforementioned PC board in thecatheter handle. Suitable temperature sensors and controllers whichcontrol power to electrodes based on a sensed temperature are disclosedin U.S. Pat. Nos. 5,456,682, 5,582,609 and 5,755,715.

[0118] Finally, the electrodes 82 and temperature sensors 83 can includea porous material coating, which transmits coagulation energy through anelectrified ionic medium. For example, as disclosed in U.S. applicationSer. No. 08/879,343, filed Jun. 20, 1997, entitled “Surface Coatings ForCatheters, Direct Contacting Diagnostic and Therapeutic Devices,”electrodes and temperature sensors may be coated with regeneratedcellulose, hydrogel or plastic having electrically conductivecomponents. With respect to regenerated cellulose, the coating acts as amechanical barrier between the surgical device components, such aselectrodes, preventing ingress of blood cells, infectious agents, suchas viruses and bacteria, and large biological molecules such asproteins, while providing electrical contact to the human body. Theregenerated cellulose coating also acts as a biocompatible barrierbetween the device components and the human body, whereby the componentscan now be made from materials that are somewhat toxic (such as silveror copper).

[0119] Although the present inventions have been described in terms ofthe preferred embodiments above, numerous modifications and/or additionsto the above-described preferred embodiments would be readily apparentto one skilled in the art. It is intended that the scope of the presentinventions extend to all such modifications and/or additions and thatthe scope of the present inventions is limited solely by the claims setforth below.

We claim:
 1. A probe, comprising: a support body; anexpandable/collapsible tissue coagulation structure supported on thesupport body; and a mapping structure supported on the support bodydistally of the expandable/collapsible tissue coagulation structure. 2.A probe as claimed in claim 1, wherein the support body comprises acatheter.
 3. A probe as claimed in claim 1, wherein theexpandable/collapsible tissue coagulation structure comprises aninflatable structure.
 4. A probe as claimed in claim 3, wherein theinflatable structure defines an interior and the support body includes afluid lumen operably connected to the interior of the inflatablestructure.
 5. A probe as claimed in claim 3, wherein the inflatablestructure comprises a non-porous, relatively thermally conductivestructure.
 6. A probe as claimed in claim 5, further comprising: a fluidheating element located within the interior of the inflatable structure.7. A probe as claimed in claim 3, wherein the inflatable structurecomprises a porous structure.
 8. A probe as claimed in claim 7, whereinthe porous structure includes a porous region and a non-porous region.9. A probe as claimed in claim 7, further comprising: an electrodelocated within the interior of the inflatable structure.
 10. A probe asclaimed in claim 1, wherein the expandable/collapsible tissuecoagulation structure comprises a hoop structure and at least oneoperative element supported on the hoop structure.
 11. A probe asclaimed in claim 10, wherein the support body defines a longitudinalaxis and the hoop structure defines a plane perpendicular to thelongitudinal axis.
 12. A probe as claimed in claim 10, wherein the hoopstructure comprises a hoop spline and at least first and second supportsplines.
 13. A probe as claimed in claim 12, wherein the hoop structurecollapses in response to movement of the first and second supportsplines in opposite directions.
 14. A probe as claimed in claim 13,wherein the support body comprises a first support body member definingan inner lumen and a second support body member movable within the innerlumen, the first support spline is operably connected to the firstsupport body member, and the second support spline is operably connectedto the second support body member.
 15. A probe as claimed in claim 10,wherein the hoop structure comprises a hoop spline, a plurality ofsupport splines, and first and second proximally extending stylets. 16.A probe as claimed in claim 15, wherein the hoop structure collapses inresponse to movement of the first and second stylets in oppositedirections.
 17. A probe as claimed in claim 10, wherein the hoopstructure comprises a helical support structure.
 18. A probe as claimedin claim 10, wherein the at least one operative element comprises aplurality of spaced electrodes.
 19. A probe as claimed in claim 1,wherein the mapping structure comprises an expandable/collapsiblemapping basket.
 20. A probe as claimed in claim 19, wherein theexpandable/collapsible mapping basket comprises at least two splinesrespectively supporting at least two electrodes.
 21. A mapping andcoagulation apparatus, comprising: a tissue coagulation probe includinga tissue coagulation probe support body defining at least one interiorlumen, and an expandable/collapsible tissue coagulation structuresupported on the tissue coagulation probe support body; and a mappingprobe passable through the tissue coagulation probe support body lumenincluding a mapping probe support body, and a mapping structuresupported on the mapping probe support body.
 22. A mapping andcoagulation apparatus as claimed in claim 21, wherein the tissuecoagulation probe support body comprises a catheter.
 23. A mapping andcoagulation apparatus as claimed in claim 21, wherein theexpandable/collapsible tissue coagulation structure comprises aninflatable structure.
 24. A mapping and coagulation apparatus as claimedin claim 23, wherein the inflatable structure defines an interior andthe tissue coagulation probe support body includes a fluid lumenoperably connected to the interior of the inflatable structure.
 25. Amapping and coagulation apparatus as claimed in claim 23, wherein theinflatable structure comprises a non-porous, relatively thermallyconductive structure.
 26. A mapping and coagulation apparatus as claimedin claim 25, further comprising: a fluid heating element located withinthe interior of the inflatable structure.
 27. A mapping and coagulationapparatus as claimed in claim 23, wherein the inflatable structurecomprises a porous structure.
 28. A mapping and coagulation apparatus asclaimed in claim 27, wherein the porous structure includes a porousregion and a non-porous region.
 29. A mapping and coagulation apparatusas claimed in claim 27, further comprising: an electrode located withinthe interior of the inflatable structure.
 30. A mapping and coagulationapparatus as claimed in claim 21, wherein the expandable/collapsibletissue coagulation structure comprises a hoop structure and at least oneoperative element supported on the hoop structure.
 31. A mapping andcoagulation apparatus as claimed in claim 30, wherein the tissuecoagulation probe support body defines a longitudinal axis and the hoopstructure defines a plane perpendicular to the longitudinal axis.
 32. Amapping and coagulation apparatus as claimed in claim 30, wherein thehoop structure comprises a hoop spline and at least first and secondsupport splines.
 33. A mapping and coagulation apparatus as claimed inclaim 32, wherein the hoop structure collapses in response to movementof the first and second support splines in opposite directions.
 34. Amapping and coagulation apparatus as claimed in claim 33, wherein thetissue coagulation probe support body comprises a first support bodymember defining an inner lumen and a second support body member movablewithin the inner lumen of the first support body member and defining theat least one interior lumen, the first support spline is operablyconnected to the first support body member, and the second supportspline is operably connected to the second support body member.
 35. Amapping and coagulation apparatus as claimed in claim 30, wherein thehoop structure comprises a hoop spline, a plurality of support splines,and first and second proximally extending stylets.
 36. A mapping andcoagulation apparatus as claimed in claim 35, wherein the hoop structurecollapses in response to movement of the first and second stylets inopposite directions.
 37. A mapping and coagulation apparatus as claimedin claim 30, wherein the hoop structure comprises a helical supportstructure.
 38. A mapping and coagulation apparatus as claimed in claim30, wherein the at least one operative element comprises a plurality ofspaced electrodes.
 39. A mapping and coagulation apparatus as claimed inclaim 21, wherein the mapping structure comprises anexpandable/collapsible mapping basket.
 40. A mapping and coagulationapparatus as claimed in claim 39, wherein the expandable/collapsiblemapping basket comprises at least two splines respectively supporting atleast two electrodes.
 41. A probe, comprising: a support body defining alongitudinal axis; an expandable/collapsible hoop structure defining anopen interior region and supported on the support body such that thelongitudinal axis of the support body passes through the open interiorregion; and at least one operative element supported on theexpandable/collapsible hoop structure.
 42. A probe as claimed in claim41, wherein the support body comprises a catheter.
 43. A probe asclaimed in claim 41, wherein the at one operative element comprises aplurality of spaced electrodes.
 44. A probe as claimed in claim 41,wherein the hoop structure comprises a hoop spline and at least firstand second support splines.
 45. A probe as claimed in claim 44, whereinthe hoop structure collapses in response to movement of the first andsecond support splines in opposite directions.
 46. A probe as claimed inclaim 45, wherein the support body comprises a first support body memberdefining an inner lumen and a second support body member movable withinthe inner lumen, the first support spline is operably connected to thefirst support body member, and the second support spline is operablyconnected to the second support body member.
 47. A probe as claimed inclaim 41, wherein the hoop structure comprises a hoop spline, aplurality of support splines, and first and second proximally extendingstylets.
 48. A probe as claimed in claim 47, wherein the hoop structurecollapses in response to movement of the first and second stylets inopposite directions.
 49. A probe as claimed in claim 41, wherein thehoop structure comprises a helical support structure.
 50. A probe asclaimed in claim 41, wherein the hoop structure comprises a hoop splineand at least first and second radially extending support splines.
 51. Aprobe as claimed in claim 41, wherein the hoop structure comprises ahoop spline and at least first and second distally extending supportsplines that respectively define acute angles with the longitudinal axisof the support body.
 52. A probe as claimed in claim 51, wherein thesupport body includes tubular members extending distally therefrom atthe acute angle and the support splines are at least partially locatedwithin the tubular members.
 53. A probe as claimed in claim 51, whereinthe first and second support splines extend distally from the supportbody to the hoop spline and the hoop structure further includes at leastthird and fourth support splines extending distally from the hoopspline.
 54. A probe as claimed in claim 41, wherein the hoop structurecomprises at least two structural members, each structural memberconsisting of a pair of struts and a curved portion.
 55. A probe asclaimed in claim 54, wherein the hoop structure comprises fourstructural members.
 56. A probe as claimed in claim 41, wherein thesupport body defines a distal end and the hoop structure is locatedproximally of the distal end of the support body.
 57. A probe as claimedin claim 41, wherein the support body defines a distal end and the hoopstructure extends distally from the distal end of the support body.